The requirement for a surfactant where colloidal suspensions or emulsions are employed (e.g., in the preparation of latexes, microspheres, or in suspending agents used as antipollutants) is well recognized in the art. Further, it is desirable to utilize a surfactant having the highest adsorption efficiency attainable. One example is the use of such material in a polymer latex used to obtain coatings which are impermeable to the passage of moisture and gases, such as oxygen. In such systems, excess surfactant in the water phase of such latex interferes with the impermeability characteristics of the latex by producing exudates at the coating surface. Further, the surfactant frequently interferes with adhesion of the latex to the substrate being protected or with cohesion of the coating to itself (heat seal). Still further, coatings containing excess surfactants have a high level of water leachables which oftentimes precludes the use of such materials in applications such as food wraps.
It is not feasible in such applications to reduce the level of surfactant to avoid these problems as this results in an increase in surface tension and loss of wetting characteristics, as well as a reduction in stability of the latex against the action of shear and electrolytes.
A further requirement for a successful surfactant for use in colloidal suspensions or emulsions is the ability of such material to remain on the surface of the disperse phase of the colloidal suspension or emulsion in the presence of other formulating agents or when the colloidal suspension or emulsion is diluted or concentrated. It is the molecular structure of the surfactant and its method of attachment to the disperse phase of the colloidal suspension or emulsion which will determine the amount of surfactant required as well as the colloidal stability, viscosity and other rheological properties of the colloidal suspension or emulsion.
Prior known surfactant materials include the conventional nonpolymerizable, water-soluble cationic soaps as described, for example, in U.S. Pat. No. 3,322,737 and in Surfactant Science Series, Vol. 4, Cationic Surfactants, edited by Eric Jungerman, pp. 179-189 (1970), Marcel, Dekker, Inc., N.Y. In general, these materials are characterized by relatively low energies of adsorption and can easily be displaced or desorbed from a disperse phase in the presence of other materials having a higher energy of adsorption or by dilution of the suspension or emulsion.
Other types of prior known surfactants having somewhat greater resistance to desorption are the surface-active polymeric or polymerizable materials used for the preparation of latexes as disclosed, for example, in U.S. Pat. Nos. 3,177,172; 3,399,159 and 3,617,638; as well as the publication by Migranyan et al. [Vysokomolkulyarnye Soedineniya, Seriya B, 11, No. 8, 620-623 (1969)]. See also the review article by Cernikof [La Chimica e L'Industria, 52, 659-663 (1970)]. Basically, such prior art relates to the combination of monomeric materials formed into a polymer with an ionically substituted hydrophilic backbone to which is attached relatively long-chain hydrophobic groups such as are present in the conventionally used soaps. Yet another type of polymerized material, for use in latex preparation, are certain alkyl sulfide terminated oligomers as described in U.S. Pat. No. 3,498,943. These materials differ from the surfactants contemplated by the present invention in that they rely primarily on the hydrophobic thioalkyl end groups for adsorption onto the disperse phase of the latex. Such materials are polymeric analogs of conventional soaps having a hydrophilic head and a hydrophobic tail. Further, these polymers, when used to make latexes, yield products with high surface tension and are not representative of the interpolymeric surfactants of the present invention.
Other types of polymerized material for use in making latex are the interfacially spreading polyelectrolytes described in U.S. Pat. No. 3,965,032. These polyelectrolytes are devoid of pendant hydrophobic groups and thus are not representative of the present cationic polymeric surfactants.